如何在Flutter中仅为OutlineButton设置下划线边框

dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^0.1.2
  flutter/material.dart: ^1.0.0

import 'package:flutter/material.dart';

class MyButtonPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('OutlineButton示例'),
      ),
      body: Center(
        child: OutlineButton(
          borderSide: BorderSide(color: Colors.blue, width: 2.0),
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(8.0),
          ),
          child: Text('点击我'),
          onPressed: () {
            // 按钮点击事件
          },
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: MyButtonPage(),
  ));
}